Nitrogen-, phosphorus- and sulfurcontaining lubricants



United States Patent QfifiCti 3,070,546 Patented Dec. 25, 1962 Thisinvention relates to lubricant compositions, more particularly tolubricating oil compositions improved by the incorporation therein ofcertain nitrogen-, phosphorusand sulfur-containing compositions. Suchlubricant compositions are adapted especially for use in the lubricationof power-transmitting units which employ frictional clutch plates orother such surfaces.

Power-transmitting units of the above type are useful for many purposes.One such use consists of the mechanical clutch type transmission unitsfound in automotive vehicles for transmitting power from the engine tothe dilferential. Recently they have also found usage in certain newautomotive differentials. Units of this type depend upon smooth and firmengagement of clutch plates for eflicient transmission of power. Toprovide such smooth operation, the lubricant used must possess a uniquecombination of lubricating properties. Thus, in addition to the ordinaryproperties of resistance to corrosion, oxidation, and extreme pressure,oiliness, detergency, etc., the lubricant used must posses suitablefrictional properties a well. It must be capable of allowing the clutchplates to slide smoothly into contact and then to, become firmly engagedwith each other. It must not permit slipping of the engaged plates evenwhen heavy loads are applied to the unit; neither must it permitgrabbing of the plates while they are being engaged or disengaged.Failure of the lubricant to satisfy the above frictional requirementswill result in interrupted and ineflicient transmission of power, whichgenerally manifests itself in the development of a chatter-like noise.If such operation is allowed to continue for an extended period, it willresult in excessive wear and premature breakdown of the unit in use.

The development of the chatter-like noise is recognized as a reliableindication of inadequate, unsatisfactory lubrication and various methodshave been developed which will permit the measurement of such noise as ameans of evaluating the lubricant.

It is accordingly an object of this invention to provide improvedlubricant compositions.

It is another object of this invention to provide lubricant compositionsfor use in power-transmitting units.

It is. another object to provide lubricant compositions which areespecially useful for lubricating power-transmitting units employingfrictional clutch plates.

It is another object to provide lubricant compositions for automatic.transmissions.

It is also an object to provide lubricant compositions Group II metalphosphorodithioates are well-known compositions. They may be exemplifiedby barium, magnesium, strontium, cadmium, calcium, and zinc salts of aphosphorodithioic acid having the. formula:

P/ nio s'H wherein R and R are like or unlike organic radicals, eachcontaining from 1 to about 40 carbon atoms. Of these A metal salts, zincphosphorodithioates have been found to be especially effective aslubricant additives, and they are accordingly preferred for use in thisinvention. Methods for preparing phosphorodithioic acids and their metalsalts have been described in the art and need not be discussed in detailhere. The most convenient method for preparing the acid comprises thereaction of phosphorus pentasulfide with an appropriate hydroxycompound, i.e., alcohol or phenol, according to the following equation:

wherein ROH represents the hydroxy' compound. The corresponding metalsalts are obtainable simply by neutralizing the acid with a basic metalcompound such as a metal hydroxide, metal oxide, or by reaction of theacid with an elemental metal.

The particular group II metal phosphorodithioates of this invention arethose derived from phosphorodithioic acids in which there are a total ofat least about 7.6 aliphatic carbon atoms in the two organic radicalsattached to each phosphorus atom of the acid molecule. Such salts arewell-known in the art, and certain subgroups thereof are described inU.S. Patents 2,838,555; 2,689,220; 2,680,123; 2,364,283; and 2,364,284.:Those derivedfrom dialkylphosphorodithioic acids are preferred for usein the lubricants of this invention because of their particulareffectiveness in combination with the fatty amide additives. The alkylradicals commonly found in such phosphorodithioates may be illustratedby, for example, octyl, dodecyl, pentyl, isopropyl, cyclohexyl,octadecyl, methylcyclohexyl, and the like.

Specific examples of the oil-soluble group II metal phosphorodithioatesinclude: zinc dicyclohexyl phosphorodithioate, zinc diisoctylphosphorodithioate, calcium dicyclopentyl phosphorodithioate, bariumdioctadecyl phosphorodithioate, cadmium diheptyl phosphorodithioate, thezinc salt. of a mixture of 40 mole-percent of di-noctylphosphorodithioic acid and mole-percent of diisopropyl phosphorodithioicacid, the zinc salt of a mixture of equimolar amounts of di-sec-pentyl'phosphorodi-:

thioic acid and diisopropyl phosphorodithioic acid, the

barium salt of a phosphorodithioic acid, derived from a.

are those having the structural formula where R is an aliphatichydrocarbon radical having at least about 12 carbon atoms and R isselected from the class consisting of aliphatic hydrocarbon radicals andhydrogen. Especially valuable are the fatty acid amides and thenaphthenic acid amides. They may be illustrated by the amides of, e.g.,oleic acid, stearic acid, lauric acid, palmitic acid, petroleumnaphthenic acid, linoleic acid, linolenic acid, arachidic acid, andmixtures of acids such as those obtained from the hydrolysis ofvegetable or animal fats. Also contemplated are the N-substituted fattyacid amides in which the N-substituent is generally a hydrocarbonradical such as methyl, cyclohexyl, dodecyl, etc. The amides of fattyacids having about 16-24 aliphatic carbon atoms in the fatty radicalhave been found to be especially effective and accordingly theyconstitute a preferred class of amides for use in the lubricantcompositions of this invention. Specific examples of the useful fattyacid amides include: oleamide, stearamide, N-methyl oleamide,N,N-dibutyl lauramide, myristamide, palmitamide, N-cyclohexylstearamide, and mixtures of such amides. The carbon atom content of suchamides may range up to 60 or higher.

The base oils which are useful with the additive combinations of thisinvention may be any oils having lubricating propenties, irrespective oftheir source or methods of production. For the most part, lubricatingoils of petroleum origin and having viscosity values within theapproximate range of 503000 SUS (Saybolt Universal seconds) at 100 F.are most commonly used.

The amounts of the phosphorodithioate additive and the amide additivewhich should be used in the lubricants of this inventionlie withinrelatively narrow ranges of concentration. The amount of thephosphorodithioate additive is within about 0.01% to about 2% by weight,as phosphorus, based upon the weight of the final lubricant, and that ofthe amide additive is within about 0.05% to about 3% by weight. For usein most applications, the optimum amount of the phosphorodithioateadditive is within the range of concentration of 0.1%-1% by weight asphosphorus, and that of the amide additive is within the range ofconcentration of 0.l%l% by weight. Except for considerations of economy,there is usually no disadvantage in using more than the optimum amountneeded for a particular application.

The lubricant compositions of this invention are useful for lubricatinggears, bearings, torque converters, internal combustion engines, andother machines which employ relatively moving solid surfaces. They areespecially valuable, as indicated before, for use in the lubrication ofpower-transmitting units employing frictional clutch surfaces such asare found in the mechanical clutch type automatic transmission units anddifferentials of automotive vehicles. An especially efiective use ofsuch compositions is in the lubrication of the so-calle d lockingdifferential, also known as the non-slip or limitedslip differential.Such a differential is capable of locking the two driving axle shaftsinto one rigid unit and this is especially useful under drivingconditions such as those encountered in operating a car in snow or mud.By such axle-locking, the two driving wheels must spin at the same speedand consequently, unlike the conventional type, the locking differentialis capable of preventing the loss of axle torque through the freespinning of any one wheel which may happen to be driven on an icy patchof pavement for example. The locking of the axles is done through theuse of frictional clutch plates or other such surfaces attached to bothof the axle shafts, which clutch plates are capable of becoming firmlyengaged when the above driving conditions exist.

Satisfactory operation of this type of differential quite obviouslyrequires a lubricant having suitable frictional properties in additionto the ordinary lubricating properties. Hence, lubricants which areadequate for use in conventional differentials are not necessarilysatisfactory for use in the locking differential. It has now beendiscovered, however, that by the combined use in a lubricatingcomposition of the phosphorodithioate and amide additives of thisinvention, a synergistic effect is produced which is sufiicient to allowthe satisfactory performance of such differentials.

The desirable frictional properties of the lubricant compositions ofthis invention are shown by the results, summarized in Table I, of anexaggerated chattering test. In this test, the chatteringcharacteristics of a lubricant are measured in terms of the intensity ofnoise developed during the engagement of a rotating plastic frictionplate with a stationary steel friction plate while the interface betweenthe plates is being lubricated by the test lubricant. The test isconducted under conditions simulating that encountered in actualoperation of many types of commercial transmissions and clutches. Inbrief, the apparatus employed in this test consists of: (1) a carbonsteel cup (having an inner horizontal flat surface) equipped with achatter-transmitter microphone wired to an elec, tronic audio-amplifierwhich is in turn wired to an electric output recording meter formeasuring the chatterintensity, the base of the cup being used both as areservoir for the test lubricant and as one of the test friction plates;(2) a hard phenolic plastic circular friction plate mounted horizontallyon the lower end of the vertical shaft of an electric motor-driven drillpress; and (3) means for holding the steel cup in stationary positionthroughout the operation of the apparatus.

In conducting the test, a BSD-gram sample of a Mid- Continent,solvent-refined lubricating oil blend (having a viscosity value of 40SUS at 210 F. and a viscosity index value of about containing theadditive to be tested is heated in a beaker at C. for 17 hours while airis bubbled through the oil at a rate of 1 cubic foot per hour. Duringthis heating a lead strip (31 grams), a copper screen (55 grams), and aniron screen (125 grams) are immersed in the oil to promote oildegradation such as encountered in actual service of the oil in manymachines. A 4-grarn sample of the oxidized lubricant is then placed inthe steel cup and heated to approximately 200 F. The plastic frictionplate, while being rotated at a speed of about 80 rpm. on its verticalcenter axis as driven through the drill press shaft by a 0.75 horsepowerelectric motor, is lowered toward the steel cup containing the lubricantand eventually pressed under a load of about pounds into close facecontact with the base of the stationary steel cup; after about twominutes of rubbing of the friction plates to attain equilibriumconditions, a noise-intensity reading is taken on the recording meter.The noise-intensity is recorded on an arbitrary scale of from 0 to 500,0 being indicative of the complete absence of noise and 500 beingindicative of extreme noise development. On this scale a typicallubricating oil without the oil-soluble additive combinations of thisinvention gives a noise-intensity reading above 300 under the testconditions. A reduction of the noise-intensity reading to about 200 as aresult of incorporation into the oil of chemical addition agents isconsidered as a substantial improvement, and a reduction to about 90 orless is considered as an excellent improvement.

The additives employed in this test are identified as follows:

COMPONENT A.--PHOSPHORODITHIOATE ADDITIVB A-1z Zincdi(isooctyl)phosphorodithioate.

A-2: Zinc salt of a phosphorodithioic acid made by reacting phosphoruspentasulfide with an alcohol mixture of 65 mole-percent of isobutanoland 35 molepercent of isopentanol.

A-3z Barium salt of a phosphorodithioic acid made by reacting phophoruspentasulfide with an alcohol mixture of 50 mole-percent of caprylalcohol, 37.5 molepercent of 4-methyl-2-pentanol, and 12.5 mole-percentof cyclohexanol.

A4: Zinc di(tridecyl)phosphorodithioate.

A5: Zinc di(heptyl phenyl)phosphorodithoiate.

A-6: A mixture of 46 weight-percent of zinc di(isootyl)phosphorodithioate and 54 weight-percent of zinc di- (methylcyclohexylphosphorodithoiate.

COMPONENT B.-FATTY AMIDE ADDITIVE Table I GHATIERING TEST AdditivesTested Chattering Intensity Reading Lubricant PhosphorodithioateAdditive, percent by weight as phosphorus Amide Additive, percent byweight None None None None None Although the additive combinations ofthis invention are of value when used alone in a lubricating oil, it isoften desirable that the lubricant be improved not only with respect tothe friction characteristics described above, but also with respect toother properties as well. Thus,

in the lubrication of hypoid gears such as used in automotivedifferentials, the lubricant used should also possess high thermalstability and resistance to formation of corrosive degradation products,superior extreme-pressure lubricating characteristics, low pour point,resistance to foam, etc. For use in automatic or manual transmissionunits, the lubricant should further possess dispersant properties andhigh viscosity index values. These properties whenever they are calledfor, may be provided by the incorporation in the lubricating oil ofvarious chemical additives well-known in the art. Oxidation andcorrosion inhibition properties may be provided by the addition ofphosphorus sulfide-treated cyclic olefinic substances, substitutedphenolic compounds, aryl amines, and other known inhibitors. Thedesirable viscosity characteristics may be imparted to the oil by suchwellknown polymeric additives as poly(alkyl acrylates) and poly(alkylmethacrylates), iso-butene polymers, etc. Foam suppression may beeffected by the use of silicone type substances or poly(alkylacrylates). Additives which are capable of imparting superiorextreme-pressure characteristics to the oil are also well-known in theant, and the commonly employed extreme-pressure additives may beexemplified by organic sulfides and polysulfides,

xanthates, phosphorus sulfide treated fatty oils and chlorinatedhydrocarbons. Dispersant additives which are commonly used inlubricating oils are illustrated by the normal and basic metal salts ofalkyl phenols and alkyl phenol sulfides; the normal and basic metalsalts of, e.g., long chain hydrocarbon sulfonic acids, acidic reactionproducts of a phosphorus sulfide with olefin polymers, acidic reactionproducts of a phophorus chloride with chlorinated hydrocarbons, acidicreaction products of olefin polymer, sulfur, and phosphorus trichloride;normal or basic salts of long chain fatty acids, etc.

The utility of the additive combinations of this invention in lubricantsfor automotive transmissions is shown by the results of the. CadillacHydramatic Transmission Lubricant Test. In this test, the lubricant tobe evaluated is employed as the transmission lubricant in a 1956hydramatic transmission connected to a 1956 Cadillac engine operated for300 hours under'the following conditions.

Operating cycle:

15 seconds at idle. 45 seconds at 2100 r.p.m. in fourth gear at a loadof 59.5 brake horsepower (acceleration through first, second, and thirdgears). Transmission oil sump temperature: 300 F. Engine water-outlettemperature: 1604170 F. Crankcase oil temperature: 250 F.

After completion of the test, the transmission is dismantled and theamount of sludge and varnish formed are noted and rated on a numericalscale of 10 to 0, 10 being indicative of no sludge or varnish, 7.5 beingindicative of a trace of sludge or varnish formed, and 0 beingindicative of heavy sludge or varnish formation. The duration of thetest prior to the development of a chatter-like noise is also noted. Toa'Mid-Continent, solvent-refined lubricating oil blend having aviscosity of 40 SUS at F. and a viscosity index of about 95' andcontaining the usual amounts of a commercial ashless,nitrogen-containingdispersant additive, silicone-type anti-foam agent, a polymethacrylatetype viscosity-index improving agent, and wax alkylated naphthalene typepour-point depressant, there was added 0.1% by weight as phosphorus ofzinc diisooctylphosphorodithioate and 0.25% by weight of the fatty acidamide identified previously as B-l. When this lubricant was subjected tothe above test it gave a sludge rating of 7.4 and a varnish rating of8.9. There was no chatter noise for over hours.

The efficacy of the additive combinations in lubricant compositions foruse in automotive differentials is shown by the results, summarized inTable II, of the Chevrolet Power-Lola Differential Lubricant Test. Inthis test, the lubricant to be evaluated is used as the differentiallubricant in a 1956 8-cylinder Chevrolet passenger car equipped withPowerglide transmission and Power-Lek" differential (locking typedifferential). The car is driven for 15 minutes to establish equilibriumconditions, and then the development of noise noted as the car is turnedabruptly both while in forward and reverse gears. The lubricant baseused in this test is an SAE 90 mineral lubricating oil to which therehas been added the usual amounts of a commercial alkenylsuccinic acidrust inhibitor, polyalkylmethacrylate type anti-foam agent, commercialextreme-pressure additive consisting of a mixture of a chlorinatedparafiin wax and an alkyl polysulfide.

A'specific embodiment of the invention is illustrated by theincorporation into an SAE 90 mineral oil of 3.36% of chlorinatedparaflin wax (containing 50% chlorine), 2.0% (0.16% as phosphorus) orzinc di-(4-methylamyl- 2) phosphorodithioate, 0.1% of the amide mixturedesignated previously as B-l, 0.05% of an alkenylsuccinic acid preparedby the alkylation of maleic anhydride with tetrapropylene and subsequenthydrolysis of the alkenylsuccinic anhydride, and 400 ppm. of a lowmolecular weight polymer of butyl acrylate. Such a lubricant is usefulfor the purposes mentioned earlier herein.

Table II DIFFERENTIAL LUBRICANT TEST Noise Lubricant PhosphorodithioateAdditive, percent wt. as Amide Additive, percent by wt.

phosphorus Forward Reverse 1 zinc(4-methyl-pentyl-2)phosphorodithioate... 0.16 Amide identified previously 0.13 None....None.

as 9 rln 0.36 0.31 .do Do. rin 0.28 Amide of fatty acid derived 0.5 do.Do.

from tall oil. 4 0.3 Amid; 1identified previously 1 do Do.

5 zinc salt ofaphosphorodithioic acid obtained 0.64 do 0.5 do... Do.

by reaction of P155 with an alcohol mixture of 60 mole-percentisopropanol and 40 molepercent of 4 n1ethy1-pentanol2. 6zinc(4-methyl-pentyl-2)phosphorodithioate.-. .do.--- D0. 7 Scvere--Severe. R N -do do- Do.

Contains no chlorinated paraffin wax.

The use of the expression oil-soluble carboxy amide in thisspecification and in the appended claims may denote a single amide or amixture of two or more amides. By the term oil-soluble, as used herein,it is intended to indicate the property of the additive to form not onlytrue solutions with the oil to which they are added, but also theproperty to form therewith any form of substantially permanentlyhomogenous composition.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

We therefore particularly point out and distinctly claim as ourinvention:

1. A lubricant composition consisting essentially of a major proportionof a mineral lubricating oil and in combination therewith from about0.01 to about 2.0 percent by weight of phosphorus of an oil-solublegroup II metal phosphorodithioate and from about 0.05 to about 3.0percent by weight of an oil-soluble carboxy amide having the structuralformula 0 R--NHR! where R is an aliphatic hydrocarbon radical having atleast about 12 carbon atoms and R is selected from the class consistingof aliphatic hydrocarbon radicals and hydrogen.

2. The lubricant composition of claim 1 characterized further in thatthe group II metal phosphorodithioate is a zincdialkylphosphorodithioate.

3. The lubricant composition of claim 1 characterized further in thatthe group II metal phosphorodithioate is a bariumdialkylphosphorodithioate.

4. The lubricant composition of claim 1 characterized further in thatthe oil-soluble carboxy amide contains from about 16 to about 24aliphatic carbon atoms.

5. A lubricant composition consisting essentially of a major proportionof a mineral lubricating oil and in combination therewith from about0.05 to about 1.0 percent by weight as phosphorus of a zincdialkylphosphorodithioate and from about 0.1 to about 1.0 percent byweight of a fatty acid amide having from about 16 to about 24 aliphaticcarbon atoms and having the structure RCONH where R is an aliphatichydrocarbon radical.

6. The lubricant composition of claim 5 characterized further in thatthere is a total of at least about 7.6 aliphatic carbon atoms in the twoalkyl radicals of the zinc dialkylphosphorodithioate.

7. The lubricant composition of claim 5 characterized further in thateach of the alkyl radicals of the zinc dialkylphosphorodithioatecontains from about 4 to about 12 carbon atoms.

8. The lubricant composition of claim 5 characterized further in thatthe zinc dialkyl posophorodithioate is zinc dioctylphosphorodithioate.

9. The lubricant composition of claim 5 characterized further in thatthe zinc dialkyl phosphorodithioate is zinc dihexylphosphorodithioate.

10. The lubricant composition of claim 5 characterized further in thatthe fatty acid amide is oleamide.

11. The lubricant composition of claim 5 characterized further in thatthe fatty acid amide is lauramide.

12. The lubricant composition of claim 5 characterized further in thatthe fatty acid amide is a mixture of fatty acid amides having an averageof about 18 carbon atoms in the fatty radicals.

References Cited in the file of this patent UNITED STATES PATENTS2,018,758 Ellis Oct. 29, 1935 2,358,581 Lieber Sept. 19, 1944 2,364,283Freuler Dec. 5, 1944 2,710,842 Heisig et a1 June 14, 1955 2,934,499Goldschmidt Apr. 26, 1960

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PROPORTIONOF A MINERAL LUBRICATING OIL AND IN COMBINATION THEREWITH FROM ABOUT0.01 TO ABOUT 2.0 PERCENT BY WEIGHT OF PHOSPHORUS OF AN OIL-SOLUBLEGROUP II METAL PHOSPHORODITHIOATE AND FROM ABOUT 0.05 TO ABOUT 3.0PERCENT BY WEIGHT OF AN OIL-SOLUBLE CARBOXY AMIDE HAVING THE STRUCTURALFORMULA